- “Alice? Is it really you, Alice McDuff??
- “Yes, it´s me. Hi, how are you?”
- “Good, thanks. Christ, I can´t believe it… how long has it been since we last talked?”
- “Umm, I don´t know … about a year, I guess…”
- “Right, exactly! We met at London-Heathrow, I was coming back from that Norwegian research mission, and you were just leaving for the continent..”
- “Oh yes, that was… curious, really. A curious meeting on a dreadful Airport.”
- “Haha, yeah. I remember very well… you had just split up with that fellow you had been so much in love with… and I told you that from my point of view, he was a coward and that you deserved better… what was his name again??
- "Aww no, Eric, please don´t....."
- "Anyway… you were pretty sad at that time, beautifully sad if I may say…. I hope you got over him by now… you do have, have you??”
- "Hmmmm. Listen, Eric. I need your help.”
- “Anytime, baby. What can I do for you? Another emotional rescue needed, or..???”
- “What do you know about *Polarization*?"
- “Polarization”? You mean, as in “plane polarization”?
- "I don´t know, you tell me, you´re the scientist! But yeah, I guess… You know, last Friday when I drove back from work in my car, I heard on the radio that birds use polarization for their orientation… I thought that this is a very interesting phenomenom… and a good thread for a write. So I´d like to know more about it. I remembered that you have been doing some research on that stuff last year.. so, what can you tell me about it?”
- “Well, okay. You asked for it. So let´s start with some basics:
“Polarization: The simplest manifestation of polarization to visualize is that of a plane wave, which is a good approximation to most light waves (a plane wave is a wave with infinitely long and wide wavefronts). All electromagnetic waves propagating in free space or in a uniform material of infinite extent have electric and magnetic perpendicular to the direction of propagation. Conventionally, when considering polarization, the electric field vector described and the magnetic field is ignored since it is perpendicular to the electric field and proportional to it. The electric field vector may be arbitrarily divided into two perpendicular components labelled x and y (with z indicating the direction of travel). For a simple harmonic wave, where the amplitude of the electric vector varies in a sinusoidal manner, the two components have exactly the same frequency. However, these components have two other defining characteristics that can differ. First, the two components may not have the same amplitude. Second, the two components may not have the same phase, that is they may not reach their maxima and minima at the same time. The shape traced out in a fixed plane by the electric vector as such a plane wave passes over it (a Lissajous figure)... Can you follow, Alice?"
- “Sure, go on. I particularly fancy the part about the frequency and the presence or lack of synchronicity of amplitudes and phases… but please, continue.”
- "Okay. In nature, electromagnetic radiation is often produced by a large number of individual radiators, producing waves independently of each other. This type of light is described as incoherent. In general there is no single frequency but rather a spectrum of different frequencies present, and even if filtered to an arbitrarily narrow frequency range, there may not be a consistent state of polarization. However, this does not mean that polarization is only a feature of coherent radiation. Incoherent radiation may show statistical correlation between the components of the electric field, which can be interpreted as partial polarization. In general it is possible to describe an observed wave field as the sum of a completely incoherent part (no correlations) and a completely polarized part. One may then describe the light in terms of the degree of polarization, and the parameters of the polarization ellipse…”
- “…Incoherent radiation may show statistical correlation between the components of the electric field – partial polarization... Wow! This is complex and still so absolutely plausible. So in fact, there is a wide range of possible external circumstances for polarization to take place, but nevertheless the phenomenom is real and ever existing and revolving!”
- “Haha, yeah... kind of, if you wanna put it that way. But you particularily wanted to know about polarization in nature, didn´t you.”
- “That’s right. I want to know what it does to birds and bees and so on, what effects it has in everyday life.. but I also like it when you digress, Eric...”
- “Okay, Alice. Please listen and don´t interrupt me umteen times!
Polarization in nature, science, and technology: Light reflected by shiny transparent materials is partly or fully polarized, except when the light is normal to the surface. A polarizing filter, such as a pair of polarizing sunglasses, can be used to observe this by rotating the filter while looking through. At certain angles, the reflected light will be reduced or eliminated. Polarizing filters remove light polarized at 90° to the filter's polarization axis. If two polarizers are placed atop one another at 90° angles to one another, no light passes through..."
- "...no light passes through."
- "Exactly. And then, there´s polarization by scattering. It is observed as light passes through the atmosphere. The scattered light produces the brightness and color in clear skies. This partial polarization of scattered light can be used to darken the sky in photographs, increasing the contrast. This effect is easiest to observe at sunset, on the horizon at a 90° angle from the setting sun. Another easily observed effect is the drastic reduction in brightness of images of the sky and clouds reflected from horizontal surfaces, which is the main reason why polarizing filters are often used in sunglasses. Also frequently visible through polarizing sunglasses are rainbow-like patterns caused by color-dependent birefringent effects, for example in toughened glass (e.g. car windows) or items made from transparent plastics. The role played by polarization in the operation of liquid crystal displays (LCDs) is also frequently apparent to the wearer of polarizing sunglasses, which may reduce the contrast or even make the display unreadable…”
- “Oh Eric, do you think that people who wear these incredibly expensive, ugly sun-glasses are even aware of what´s happening to them when they look through those glasses? Maybe that´s a major but yet unconscious reason why so many people wear sunglasses, even when there´s no sunlight around…
But how about animals? They can perceive polarization of light without any aid, right?”
- "Don´t run out of patience, Alice! I can see you haven´t changed a bit. Concentrate!! And as I said: don´t interrupt me, please?!”
- “Aye, aye, Sir! »
- “OK, I´ll tell you in a second... listen to me... Many animals are apparently capable of perceiving the polarization of light, which is generally used for navigational purposes, since the linear polarization of sky light is always perpendicular to the direction of the sun. This ability is very common among the insects, including bees, which use this information to orient their communicative dances..."
- "Dance, little bee,
please dance for me..."
-" ...Polarization sensitivity has also been observed in species of octopus, squid, cuttlefish, and mantis shrimp. The rapidly changing, vividly colored skin patterns of cuttlefish, used for communication, also incorporate polarization patterns, and mantis shrimp are known to have polarization selective reflective tissue. Sky polarization can also be perceived by some vertebrates, including pigeons, for which the ability is but one of many aids to homing…”
- “An aid to homing…!!! Aw, this is stunning, really. But Eric… what about humans? I mean… do you think that humans are somehow influenced or guided by Polarization??"
- “Well, as far as we know, generally they are not. Some of us may be, though. The naked human eye is weakly sensitive to polarization, without the need for intervening filters. Polarized light creates a very faint pattern near the center of the visual field, called "Haidinger´s brush". This pattern is very difficult to see, but with practice one can learn to detect polarized light with the naked eye.”
- “Oh. I see. It needs continuous practice and perseverance. Things that most people never get ´round to.”
- “Right, you got it! Well, do you need to know more, or is it enough for a start.”
- “It is enough for today. Thank you so much! I have to digest and think about all this. I might also gather some further information on this on my own and ding you again for explanation in case I don´t manage to cope with it.”
- “You´re always welcome, Alice. I´m glad if I was helpful. But tell me… will you let me know about your write when you´ve finished it?"
- “Of course! You´ll be the first to read it, Eric.”
- “That´s almost all I wanted to hear, honey. Tho... Alice?"
-"Hmm?"
- "You still love that bastard, don´t you?"
(to be continued...)
Special thanks to: Wikipedia, the one in a million!
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